This invention pertains to a liquid silicone rubber composition for a lubricant seal. More specifically, this invention pertains to a liquid silicone rubber composition for a lubricant seal, characterized by the fact that it has high stability against lubricant that has been subjected to thermal and oxidative degradation.
Silicone rubber has high heat resistance, high cold resistance, and low compression set. Consequently, it is widely used to form seals for use in automobiles, ships, and industrial machines. For the various types of seals, including rocker cover seals, oil pan seals, oil filter seals, shaft seals, and other seals in direct contact with lubricant, the resistance to lubricant that has been degraded by heat and oxidation should be high. That is, these seals are required to display high stability to the acid components generated by the degradation of the lubricant, to residues of various additives, and to oxygen dissolved in the lubricant. Conventional silicone rubber does not have as good of stability in such an environment as is sometime desired.
In consideration of this problem, various methods have been used in efforts to increase the oil resistance of the silicone rubber composition by adding various types of basic substances into it. For example, Japanese Kokai Patent Application No. Sho 571982!-76055 discloses a method in which magnesium oxide powder is added into a silicone rubber composition that is cured by a condensation reaction so as to obtain a silicone rubber composition which can be cured at room temperature and which has a high oil resistance. Also, Japanese Kokai Patent Application No. Hei 31991!-149260 discloses a method in which magnesium oxide powder is added into a silicone rubber composition that is cured in the presence of a platinum catalyst so as to obtain a silicone rubber composition with a high oil resistance.
However, for the silicone rubber prepared using the first-mentioned method, a long curing time is needed at room temperature to obtain the silicone rubber. The workability is thus poor, and the obtained silicone rubber has low mechanical strength.
For the latter method, when a large amount of magnesium oxide powder is added, a highly basic substance, the platinum catalyst may be poisoned. In addition, in the presence of the organohydrogenpolysiloxane, the composition may begin to cure during storage. Even when the material is stored as a 2-part liquid system, it is still impossible to guarantee a high storage stability and a long pot life, and it is impossible to increase the amount of the magnesium oxide powder added. Consequently, high oil resistance cannot be realized and therefore the durability of the cured silicone elastomer is poor when used under the severe conditions of thermally and oxidatively degraded lubricants.
The purpose of this invention is to provide a type of liquid silicone rubber composition for a lubricant seal characterized by having good storage stability and long pot life before curing, and after it is cured having good stability and ability to maintain good rubber elasticity even in the presence of lubricant that has been subjected to thermal and oxidative degradation.